[英]RunTime exception on Convert.ChangeType with List<>
I am running into a RunTime Exception while trying to run a List (cast as object) through Convert.ChangeType. 我在尝试通过Convert.ChangeType运行列表(作为对象广播)时遇到了运行时异常。 This is basically the setup: 这基本上是设置:
using System;
using System.Collections.Generic;
public class Program
{
public static void Main()
{
List<string> list = new List<string>{ "1", "2", "3"};
Utils utils = new Utils();
utils.ChangeType(list, typeof(List<int>));
Console.WriteLine("Done!");
}
}
public class Utils
{
public object ChangeType(object obj, Type type)
{
return Convert.ChangeType(obj, type);
}
}
This generates the following exception: 这将产生以下异常:
Run-time exception (line 19): Object must implement IConvertible.
Stack Trace:
[System.InvalidCastException: Object must implement IConvertible.]
at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
at System.Convert.ChangeType(Object value, Type conversionType)
at Utils.ChangeType(Object obj, Type type) :line 19
at Program.Main() :line 10
I have no clue how to fix this. 我不知道如何解决这个问题。 I think I should cast object obj in Utils.ChangeType to a list of a generic type if it is a list, but I cannot get that to work. 我认为我应该将Utils.ChangeType中的对象obj转换为泛型类型的列表(如果它是列表),但是我无法使它正常工作。
Does anyone know how to fix this issue? 有人知道如何解决此问题吗?
I fixed the issue by adding the following check to Utils.ChangeType: 我通过向Utils.ChangeType添加以下检查来解决此问题:
if (IsList(obj))
{
List<object> objs = ((IEnumerable)obj).Cast<object>().ToList();
Type containedType = type.GenericTypeArguments.First();
return objs.Select(item => Convert.ChangeType(item, containedType)).ToList();
}
With IsList being a generic function in Utils to check if object is a List<>. IsList是Utils中的通用函数,用于检查对象是否为List <>。
See the updated fiddle . 请参阅更新的小提琴 。
As the exception states, the object you are trying to use convert on does not implement IConvertible. 作为异常状态,您尝试在其上使用convert的对象未实现IConvertible。 You are trying to convert a list of strings to a list of ints, and the list type is not implementing the required interface. 您正在尝试将字符串列表转换为整数列表,并且列表类型未实现所需的接口。
String and int types do implement this interface, so you can do it like this: 字符串和整数类型确实实现了此接口,因此您可以这样执行:
List<string> list = new List<string> { "1", "2", "3" };
Utils utils = new Utils();
var result = list.Select(o => (int)Convert.ChangeType(o, typeof(int)));
Console.WriteLine("Done!");
Or more concisely: 或更简而言之:
List<string> list = new List<string> { "1", "2", "3" };
Utils utils = new Utils();
var result = list.Select(Int32.Parse);
Console.WriteLine("Done!");
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